In order to perform transmission quality determination of whether desired transmission quality can be maintained when a signal is transmitted from a node to another node in an optical communication network, various pieces of information about the optical communication network are used. Here, transmission quality includes a bit error rate, a Q value, and a delay time.
The pieces of information used for transmission quality determination are as follows:    (1) The type, length, loss, chromatic dispersion coefficient, dispersion slope coefficient, and polarization mode dispersion coefficient of an optical fiber connecting nodes,    (2) The noise characteristic of an optical amplifier disposed at each node,    (3) Optical power input into a transmission path (optical fiber),    (4) The characteristic of a dispersion compensator disposed at each node,    (5) The characteristic of a transceiver,    (5-1) The bit rate and modulation method of a transmission signal,    (5-2) Optical Signal-to-Noise Ratio (OSNR) and error rate characteristics for chromatic dispersion and polarization mode dispersion,    (5-3) Error rate characteristic for the deterioration of a waveform caused by various nonlinear optical effects occurring in an optical fiber, and    (5-4) Error rate characteristic for the deterioration of an optical waveform passing through a wavelength add/drop filter at an Optical Add/Drop Multiplexer (OADM) node.
In order to accurately estimate transmission quality, transmission simulation is performed using these pieces of information. However, in the transmission simulation, it takes much time, for example, several days, to obtain a result of mathematical calculation. In addition, a calculating machine is used for the mathematical calculation.
Accordingly, instead of the transmission simulation, a method using a network design rule is often performed. The network design rule includes the database of the relationship between each of various combinations of parameters for network design and transmission quality. Using the database and a relatively simple mathematical expression, transmission quality is simply estimated.
Thus, a design procedure specified to estimate transmission quality without transmission simulation is called network design rule. That is, with the network design rule, it is possible to perform transmission quality determination of whether desired transmission quality of an optical signal transmitted from a node to another node can be maintained without performing transmission simulation.
A communication network has a network resource including at least one service domain. The service domain includes a user terminal and a controller for controlling the transmission of a data stream between the user terminal and a network node at predetermined service quality. Service quality depends on a Service Level Agreement (SLA) established between a user and the service domain. The service quality is processed by the controller and is converted into the set of policies to be employed. The policies include a policy for the selection and allocation of a network resource capable of transmitting a data stream at selected service quality. These techniques are disclosed in, for example, Japanese Laid-open Patent Publication No. 2002-319970.
At each of a plurality of points set in a design target section, a regenerative repeater or a linear repeater is disposed on the basis of the amounts of loss in a segment between a transmission terminal station and an adjacent point, a segment between two adjacent points, and a segment between a receiving terminal station and an adjacent point. In a 3R section, the amount of loss with which an optical signal transmitted from the transmission terminal station or the regenerative repeater disposed on the transmission side of the 3R section can be transmitted without being amplified by the linear repeater is calculated as a 1R target value. In the 3R section, the amounts of loss in segments are accumulated starting from the end on the transmission side to a direction apart from the transmission terminal station. The cumulative amount of loss and the 1R target value are compared. It is determined whether two segments are coupled to one segment without disposing a linear repeater on the basis of a result of the comparison. Thus, the linear repeater and the regenerative repeater are appropriately disposed. These techniques are disclosed in, for example, Japanese Laid-open Patent Publication No. 2004-297502.
A communication network is divided with nodes to obtain linear design sections, and the removal priority of regenerative repeaters at nodes at both ends of each of the design sections is stored. A linear repeater or a regenerative repeater is disposed at each node so that a signal can be transmitted in each design section and a higher margin of receiving signal quality is provided for a node having a high regenerative repeater removal priority. When a signal can be transmitted between two adjacent design sections without disposing a regenerative repeater at a boundary node, the regenerative repeater is removed. These techniques in a network design apparatus are disclosed in, for example, Japanese Laid-open Patent Publication No. 2005-86521.
The configuration of an optical communication network using an optical transmission apparatus is shifted from a point-to-point network configuration in the related art to a ring or mesh network configuration. FIG. 1 is a diagram illustrating the configuration of an example of a point-to-point network. FIG. 2 is a diagram illustrating the configuration of an example of a ring network. Referring to FIG. 1, nodes N1 to N4 are linearly connected to create a network.
In the ring network illustrated in FIG. 2, nodes N1 to N6 form a relatively small network NW1 and nodes N7 to N12 form a relatively small network NW2. These two networks are connected to each other via optical hub nodes N4 and N7. In such a relatively large ring or mesh network, different optical transmission systems are sometimes provided for networks. Different optical transmission systems are, for example, optical transmission systems created by different manufactures or optical transmission systems that are created by the same manufacture but are designed in accordance with different network design rules.
Referring to FIG. 2, it is assumed that the network NW1 including the nodes N1 to N6 is designed in accordance with a network design rule #1, and the network NW2 including the nodes N7 to N12 is designed in accordance with a network design rule #2. The nodes N4 and N7 are the same apparatus, and a single apparatus is called the node N4 in the network NW1 and the node N7 in the network NW2.